How can I extend my C partition with free space?

Recently, I have checked my partition capacity in Disk Management and found there are 10GB of unallocated space. So, in order to make full use all my drive space, I decide to extend my C partition with the unallocated space. But, I am not really familiar about the computer and drive stuff. So, is it possible for me to extend it with the free space? What should I do? Any suggestion could be appreciated! Thanks!

Here are two ways for you:
1). If the unallocated space is coincidentally adjacent this C partition, you can directly right click C partition to extend it in Disk Management.
2). But, if it is not behind your c partition, you also can apply some partition resizing tools like IM-Magic Partition Resizer Free, GParted and Active Partition Master, etc.
No matter which one you choose to use, always firstly back up everything important well in case of data loss.

I have ever had some success to extend my system partition with the guidance of a video tutorial: https://www.youtube.com/watch?v=6jCeT7CbsKk
Of course, never forget to make data backups at first, in case of data loss.
I hope this also can help you out.